Mass Effect was a knockoff of Knights of the Old Republic. The inventory system was mostly ineffectual, because the weapons weren't different. You picked the gun with highest stats (after playthrough one this was even worse. Get money, buy Spectre guns, done). You even get force push with biotics! No classes had any signature skills, there wasn't much difference between an adept and vanguard at high levels because barrier was the most effective for both, almost outstripping the soldier's Immunity, which was all they had.
I don't know where poorly developed squadmates in 2 comes from, as learning about your team via their missions is 80% of the game. Garrus in 1: hunt down a scientist that escaped from the Citadel. Garrus in 2: comes to terms with his failure as a team leader, the death of all those under his command, being a washout as a C-Sec/Specter, possibly Shepard's feelings for him. He was in both, so let's take a secondary squaddie for single-game development. Kaiden: all of his issues revolve around biotic training and history. He has no major developments apart from possibly Shepard's romantic intentions and a few headaches. Jack: begins as a wretched prisoner who comes from a life of abuse and neglect. As the story progresses, she seems to find something worth fighting for, to the point of in the last mission, calling Shepard "Commander" and develops some purpose in life. She actually, you know.... develops.
I'd even say the RP possiblities for Shepard are expanded in 2, as on a few occasions there's multiple options for paragon/renegade variance, instead of blue text/red text/neutral. If you want to play a hardass who also genuinely cares for his team, there are additional options to support that. The extent of this in 1 was mostly limited to blue (egalitarian, tolerant) or red (pragmatic, racist). The only nod to this that I recall from multiple plays of 1 was, dialogue changed depending on your paragon/renegade status and whether the council survived.
Regarding lots of empty hallways... plot missions aside, all of ME1 was 2 or 3 buildings with the crates moved around. Or that one ship design... with the crates moved around. Or that cave, with rocks/crates moved around. Oh, 2 also had a fight composition besides "lots of soldiers" or "lots of geth."
Don't get me wrong, I enjoyed 1, but it wasn't some rich bastion of RPG's. No matter what, you're a soldier, and you're the hero. You shoot things. Sometimes you talk, but that's between shooting things. 2 just gave up cumbersome, largely irrelevant inventory management in favor of a more detailed tactical system, and made class/squad choice more meaningful with greater focus on individual powers and using your squad correctly. It's two different approaches, one garnered more positive feedback, so they stuck with it.